x2 my expedition had the same problem. they work off of vaccume, there are relays and all the vac lines pass side fender by the power box. very rarely do the tcases have issues of not going into 4wd in my experiance. start with making sure the actuator is free and can move then hit 4x4 and pull the vac lines and make sure one has vac. also if those get swapped around at the actuator, when you hit 4x4 the front end actually disengages, ask me how i know haha 4 hrs of being stuck. if you need help let me know ive delt with those alot. and im right in hartland i can come help you